Question

I’m building a small internal phone number extension list.

In the database I have two tables, a people table, and a numbers table. The relationship is a one-to-many respectively.

I want to display the results in a single HTML table with one person per row but if they have multiple numbers it shows those in a single column with a rowspan on the person row to compensate.

Now, to get the results from the database to work with, I can either do:

(pseudocode)

SELECT id, name
FROM people

foreach result as row {
  SELECT number
  FROM numbers
  WHERE numbers.person_id = row['id']
}

This would mean that I’m doing one query to get all users, but then if I have 100 users, I’m performing 100 additional queries to get the numbers for each user.

Instead I could do it like this:

(pseudocode)

SELECT number, person_id
FROM numbers

SELECT id, name
FROM people

foreach people as person {
  echo name
  foreach numbers as number {
    if (number.id = person.id) {
      echo number
    }
  }
}

So, essentially it is doing the exact same thing except instead I do two queries to get all the results into arrays and then loop through the arrays to format my tables.

Which method should I be using or is there a better way to do this?

Answer 1

The common way is to do a regular JOIN:

SELECT id, name, number
FROM people, numbers
WHERE people.id = numbers.person_id;

You can either add an ORDER BY to get the numbers in order, or you could create an array with a single pass over the resultset, and then loop through that array.

You can also consider a GROUP_CONCAT to concatenate all the numbers for the same person:

SELECT id, name, GROUP_CONCAT(number SEPARATOR ', ')
FROM people, numbers
WHERE people.id = numbers.person_id
GROUP BY people.id;

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Since you are even asking this question: I cannot stress the fact that you should pick up an introductory book on database design. It helped me wonders to learn the theories behind relational databases.